Thermally controlled retarded relay



y 14, 1957 'r. J. RlCHARDS 2,792,533

THERHALLYTONTROLLED RETARDED RELAY Filed Jan. 8, 1956 IN VENT OR f/Mms'Jilzwdrdg I BY 4 ATTORNEY United States Patent 2,792,533 THERMALLYCONTROLLED RETARDED RELAY Thomas J. Richards, Los Angeles, Calif.

Application June 8, 1956, Serial No. 590,201 11 Claims. (Cl. 317-132)This invention relates to retarded relays of the thermally controlledtype, especially adapted for applying a time controlled reduced startingvoltage to electric appliances, such as radios, television sets,electric motors, etc.

One object of the invention is to provide a retarded relay of thecharacter indicated which dispenses with the use of electromagnets andrelies for its operation entirely upon thermally responsive elements soarranged as to be independent of ambient temperature variation.

Another object is to provide a relay of the character indicated whichcan be accurately adjusted for different time intervals of retardation.

A further object is to provide, in a relay of the character indicated, acircuit arrangement whereby an intial starting current of the requiredstrength may be obtained for the heater for the thermally responsiveelement and that current, after a predetermined time interval,automatically reduced to a lesser amount just sufiicient to maintain theheater in its heated condition.

A still further object is to provide a thermally controlled retardedrelay whereby the same delay may be obtained for a wide range of loadswithout requiring adjustment of the thermostat contacts.

The various further objects and advantages will appear from thefollowing detailed description and the features of novelty will beparticularly pointed out in the claims.

In the accompanying drawing, the figure illustrates diagrammatically anelectric circuit of a preferred embodiment of this invention.

Referring in detail to the drawing, my improved thermally retarded relayis illustrated as applied to an electric appliance, such as a televisionset TV, provided with its usual starting switch S. One terminal of theset may be connected directly to one side 10 of the power line 10, 12,while the other terminal is connected to the other side 12 of the powerline through my novel thermally retarded relay.

For applying a reduced starting voltage to the set TV, the side 12 ofthe power line is connected by wire 14 to one terminal 16 of anoninductively wound heater coil 18, the other terminal 20 of the heatercoil being connected by wire 22 to the stationary extremity 24 ofbimetallic strip 26, about which the heater coil 18 is wound. Wire 22 isfurther connected to one terminal of a resistor 28, the other terminalof resistor 28 being connected to one of the lead-in wires 30 of theelectric appliance, indicated for example as television set TV. Theother lead wire 32 of the appliance may be connected directly to theother side 10 of the power line.

From the circuit thus far described it is clear that, when the switch Sof the TV set is closed, a reduced voltage will be applied to the set byreason of the voltage drop through series resistance 28 and the heatercoil 18 in series with said resistor leading to the side 12 of the powerline. Immediately upon closing of the circuit by switch S the currentpassing through heating coil 18 will cause it to heat up, thus causingbi-metallic strip 26 to become ICE 2 heated. The heating of bimetallicstrip will cause it to flex to the left until, after a predeterminedtime interval, its movable extremity, carrying 'a manually adjustablecontact 34, makes contact with contact element 36 disposed at themovable extremity of a second bi-metallic thermostat strip 38. Contact36 is connected by a flexible wire 40 to lead-in wire 30 of theelectrical appliance TV. Thus it is seen that, after the predeterminedinterval required to heat up bi-metallic thermostat strip 26sufiiciently for it to expand until it makes contact with contact 36,the resistor 28 is shunted by wire 22, connected to stationary terminal24, bi-metallic 26, contacts 34, 36, and wire 40 connected to lead-inwire 30 of TV. This by-passing of the current around resistor 28 permitsmore current to pass through heater coil 18, causing it to heat up tohigher temperature and thus imparting additional heat to bi-rnetallic26, causing its movable extremity to bend further, carrying along withit contact 34 and contact 36 of bi-metallic 38, flexing the latter untilcont-act 36 makes contact with manually adjustable contact 42 ofbi-metallic strip 44. Contact 42 is connected by a flexible wire 46 toterminal 48 of variable resistor 50. The movable contact 52 of variableresistor 50 is connected by wire 54 connected to wire 14 leading to side12 of the power line.

From the above connections it is seen that after the predeterminedinterval of time above referred to required to heat up bi-metallic strip26, the heating of the latter is increased by the increased currentthrough heating coil 18, until strip 26 expands sutficiently to carrycontact 36 along with contact 34 so as to make contact finally withcontact 42. In this way variable resistor 50 is brought into the circuitto shunt around heater coil 18. This shunting of the heater coilaccomplishes two purposes firstly, it puts the full required voltageupon the electrical appliance TV, after the required interval requiredto .permit the set to gradually heat up; and secondly, it reduces theamount of current through the heater coil to an amount just suflicientto maintain its heat. This heat maintaining current is considerably lessthan the current required to initially bring the heater coil andbimetallic 26 up to the required temperature to secure the necessarymovements of the contacts as above described.

For the purpose of obtaining a quick adjustment of the current throughthe heater coil 18 in accordance with the amount of load imposed on thecircuit by the electric appliance, a variable resistor 56 is connectedto shunt around heater coil 18, the stationary terminal 58 of variableresistor 56 being connected to wire 22 and the adjustable terminal 60being connected to wire 14. Thus the initial heating current taken byheater coil 18 can be adjusted to the required amount by adjustingmovable contact 60 of variable resistor 56, while the finalheatm'amtaining current is adjusted by movable contact 52 of variableresistor 50.

If it should be required to vary further the retardation of the time ofthe final closing of the circuit to apply the full voltage to theelectric appliance the manually adjustable contacts 34 and 42 may beadjusted, so as to vary the amount of expansion of bi-metallic strip 26required to complete contact with contacts 36 and 42. This makes mythermal relay capable of application for regulation of appliances havinga wide range of loads.

In order to render my improved thermal relay independent of ambienttemperature variation, the three bimetallic strips 26, 38 and 44 havetheir high expansion sides facing in the same direction and are equallyresponsive to ambient temperature variation. Thus, no matter what theoutside temperature may be, :all of the three bi-metallics will beequally afiected thereby, and the relative positions of the movableextremities thereof will not be varied by such temperature variation.

synapse It will. thus be seen that I have provideda retarded relay ofthe thermally controlled type which: dispenses entirely with the use ofelectromagnetically operated circuit closing elements; may be, adjustedto secure exactly any required degree of retardation for a wide range ofloads; is unafiected by ambient temperature variation; uses a minimum ofheating current in prolongedoperation; and is composed of fewinexpensive parts, reliable, in operation, and easy to assemble.

Having described my invention, I claim:

1. A thermal relay for applying time controlled reduced startingvoltages to electric appliances, comprising a series of three adjacentbi-metallic thermostatic strips having their high expansion sides facingin the same direction and their movable extremities bearing contactsnormally serially spaced from one another; a resistance heater elementadjacent the first of said strips adapted to be connected to one side ofa power, line; means for manually regulating the heating current in saidheater element; connections including a resistor adapted for insertingsaid heater element in series with the electric appliance to becontrolled; the stationary end of said first bi-metallic strip beingelectrically connected to a junction between said heater and one end ofsaid resistor; a contact on said second strip being electrically coupledto the other end of said resistor, one terminal of said electricappliance being adapted for direct manual connection to the other sideof the power line; the contacts of the movable ends of said first andsecond bi-metallic strips being adapted to make contact with one anotherafter a timed interval subsequent to the closing of the power linecircuit through said electric appliance in series with the heaterelement, the heating of the first metallic strip by said heater causingmovement of the movable end of said first bi-metallic strip andshort-circuiting said resistor; the increased current through saidheater causing further timed movement of the contact of the firstbi-metallic strip, urging the contact of the second bimetallic intocontact with the movable contact of said third bi-metallic; said thirdbi-metallic contact being connected through a second resistor to oneside of the power line; said second resistor shunting said heaterelement to reduce the heating current therethrough and placing the fullrequired potential upon the appliance after a timed interval subsequentto the manual closing of the power line.

2. A thermal relay as defined in claim 1, including means for adjustablyvarying the spacing between said movable contacts.

3. A thermal relay as defined in claim 1, wherein said currentregulating means is a variable resistor shunting said heater element andin series with said appliance.

4. A thermalrelay second mentioned resistor is manually variable.

5. A thermal relay as defined in claim 4, wherein said currentregulating means is another manually variable resistor shunting saidheater element and in series with said appliance.

6. A thermal relay as defined in claim 1, wherein said three bi-metaliicstrips render the timing of the relay independent of variation inambient temperature.

7. A thermal relay including a series of three bimetallic strips havingtheir high expansion sides facing in the same direction; the movableextremities of said as defined in claim 1, wherein said strips bearingcontacts normally spaced from one another but adapted to make seriatimcontact with one another upon movement of the movable extremity of thefirst bi-metallic strip of the series; an electric heater element forthe first bi-metallic strip; a resistor connected between said heaterelement and the power line adapted to include in series said electricappliance upon manual closing of the circuit to apply a reduced voltageto said appliance for a predetermined time including the time ofmovement of the movable contact of said first bi-metallic strip to makecontact with the second bi-metallic strip; connections between saidsecond bi-rnetallic strip and said appliance, said resistor and heaterfor short circuit-ing said resistor, thereby increasing the impressedvoltage on said appliance and increasing the current through said heaterwhen said first bi-metallic makes contact with said second bi-metallic;and connections between said movable contact of said third bi-metailicstrip with the power line for placing the full required voltage upon theelectric appliance and including means-for shunting the heater elementsufficiently to reduce its heating current after the three movablecontacts have completed contact with one another by continued timedmovement of the movable end of the first bi-metallic strip after makingcontact with said second bi-metallic strip.

8. A thermal relay as defined in claim 7, including means for manuallyadjusting the spacing of said first and second movablecontacts.

9. A thermal relay as defined in claim 8, including means for manuallyadjusting the spacing of said second and third contacts.

10. A thermal relay as defined in claim 9, wherein said threebi-metallic strips render the timing of said relay independent ofambient temperature variation.

11. A thermal relay for applying time controlled reduced startingvoltages to an electric appliance comprising an electric circuitincluding a bimetallic thermostatic strip, a resistance heater elementadapted to be placed in series with said appliance disposed adjacentsaid thermostatic strip; means for applying a reduced starting voltageto said appliance including a resistor disposed in serie with saidresistor heater; means operated by the expanding movement of saidbimetallic strip due to the heating thereof for short circuiting saidresistor so as to apply an increasing voltage to said appliance andincreased heating current to said resistance heater, causing furthermovement of said bimetallic; and means operated by said further movementof said bimetallic strip for applying maximum voltage to said appliance,said last mentioned means including means'for shunting said resistanceheater so as to reduce the heating current thereof to a degree justsufficient to maintain the bimetallic strip substantially in its extremeposition of movement.

References Cited in the file of this patent UNITED STATES PATENTS1,738,540 Replogle Dec. 10, 1929 2,060,494 Gamel Nov. 10, 1936 2,329,119Jacobs Sept. 7, 1943 FOREIGN PATENTS 419,822 Great Britain Nov. 15, 1934

